The present invention relates to a steel material for induction hardening capable of direct cutting. More specifically, the invention relates to a steel material which can enjoy high cuttability without being annealed, so that it can be cut or rolled directly after it is milled, and which also enjoys satisfactory high-frequency induction hardenability, so that it is adapted particularly for use as a material for a drive shaft of an automobile.
Conventionally, a drive shaft of an even-speed joint is manufactured as follows. SAE-1541, for use as a steel ingot to be milled, is annealed or spheroidized to have improved cuttability, then cut or roll-finished into a predetermined shape, and finally subjected to induction hardening.
SAE-1541 is poor in cuttability, and, it will shorten the life of a cutting tool, and consume plenty of heat energy during heat treatment in the process preceding the machining processes. Thus, the SAE-1541 is not a very economical material.
Presently available, in consideration of these circumstances, is a steel ingot (e.g., ingot of JISS40C) whose cuttability is improved by reducing the manganese content of the SAE-1541. This steel ingot, however, is subjected to drawbacks including poor induction hardenability and variation in the depth of the case after hardening.